Research of vibration control method on turbine bent rotor. GUO Yu-jie, ZHANG Wen-tao

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1 Applied Mechanics and Materials Online: ISSN: , Vols , pp doi: / Trans Tech Publications, Switzerland Research of vibration control method on turbine bent rotor GUO Yu-jie, ZHANG Wen-tao HAEPC Electric Power Research Institute, Zhengzhou Henan ,China Keywords: Turbine;Bend;Dynamic balance;vibration control Abstract. According to bent position and size on two HP-IP bent rotor,and combined with maintenance schedule,this paper puts forward two vibration control methods of low speed dynamic balance on site and high speed dynamic balance after turning.for the bent position in the turbine middle,on the basis of mode decomposition in bent rotor,the research show that balance weight according to a scale in the both ends and middle mainly of the turbine can achieve good results. Preface In recent years,steam turbine generator develop toward the large capacity and high parameter direction,the rotor length is also becoming more slender. But, in order to shorten the length of shaft system, reduce the cost and improve the economy, the domestic and foreign turbogenerator manufacturers generally adopts the high pressure - medium pressure rotor of integration structure mode. According to statistics, by the influencing factors of high inlet steam parameter and small dynamic - static clearance,the HP-IP Rotor happen permanent deflection easily. There are many reasons that can cause permanent deflection of turbine rotor.they can be divided into impact and rub on rotational rotor and other reasons.the other reasons include high temperature rotor soaked in the water,shaft stress release and nonsynchronous closing[1].the reports and research papers about this field are more and play a very good role for preventing rotor bend accident to a certain extent.but,besides analysis to find out the reasons of permanent deflection,the vibration control methods of turbine rotor permanent deflection should be still lucubrated further. There are main two vibration control methods of bent rotor.one is the straightening shaft which is gradually reduced because of temperature control being very difficulty and having a certain risk.another kind is dynamic balance that can be divided into the dynamic balance on site,low speed dynamic balance and high speed dynamic balance in factory.vibration control method of dynamic balance is simple and feasible.according to the balance compensation of bent rotor, literature [2] puts forward pre-balance of turbogenerator which counter weight should be implemented in advance before unit start-up based on the unit vibration history and the feature analysis,which is a new attempt.according to the balance compensation of bent rotor,literature [3] takes dynamic balance on the high speed dynamic balancing machine that reduced the shaft vibration value and attained operation requirements. According to two turbine HP-IP bent rotor,this paper puts forward and summarizes two different vibration control methods,and puts forward counter weight model on three plane at the same time. The rotor bend and treatment condition on the first unit Vibration condition. This unit is imported type home-made 330MW,steam turbine type is integrated HP-IP cylinders,two cylinders two exhaust,single shaft,single extraction and thermal power unit,and the generator cooling mode is water-hydrogen-hydrogen.there are six All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, (ID: , Pennsylvania State University, University Park, USA-11/05/16,10:11:55)

2 Applied Mechanics and Materials Vols bearing(fig.1),# 1 and # 2 bearing are used for supporting high pressure rotor,# 3 and # 4 Cylinder bearing used for supporting low pressure rotor, # 5 and # 6 bearing used for supporting generator rotor. Fig.1 Unit shaft system The layout of vibration measuring points are that two eddy current sensors are installed separetely in bearing #1~#6.The two eddy current senor are mutual perpendicular,looking from turbine to generator,left 45 for x direction,right 45 for y direction. The unit commissioning date was in 2006 and B-level maintenance was carried out in 2008.Since 2009,critical vibration was always very big during the start-up,it was an important hidden trouble of safe start-up,and sometimes unit even triped resulting from vibration protection action.the normal start was seriously influenced. The interim measures of improving rate of rising and relaxing shaft vibration protection value were forced to take. Fig.2 shows bode graph which 1y shaft vibration changes with speed.the 1x shaft vibration maximal value is 204μm and 1y shaft vibration maximal value is 253μm during the start up and speed process. Fig.2 1y shaft vibration bode graph It can be seen that the unit vibration characteristics are as follows:vibration frequency is fundamental frequency,vibration property is forced vibration;it mainly manifests in the critical speed of HP-IP rotor,and the vibration value is not very big with load.;the critical vibration repeatability is well in many start up and speed down process, the characteristics of vibration and phase change along with the speed conforms to general rule, the first-order vibration mode is a typical "bow" bend. Rotor bent condition and vibration control. From May7 to June 30 in 2012,during overhaul of the unit,about 0.08mm bend on the medium pressure steam inlet of the HP-IP rotor was found after the cylinder was open[fig.3]. According to the inspection mark and operation condition on site,it was analyzed that the reason of rotor bend is rub impact.

3 896 Applied Mechanics and Materials I Fig.3 Bend of turbine HP-IP rotor Shaft bend is refers to deviation between center of mass attachment of each section and shaft geometric center attachment,the vibration characteristics of bent rotor is similar with quality eccentric rotor, which can both produce exciting force whose frequency is the same as speed frequency and that can make the rotor producing synchronous eddy.therefore,bent rotor can be diposed through dynamic balance. Considering that unit overhaul time limit is nervous,vibration control method is low speed balance on site,and the balancing speed is 181r/min.1.242Kg was added in the front end of turbine and 2.12Kg was added in the back end of HP-IP rotor.using the rotor dynamic theory and according to the characteristic of the first-order vibration,the added weight were to redistribute.finally,0.852kg was added in the front end,1.588kg was added in the middle and 0.899Kg was added in back end of of HP-IP rotor,the adding proportion were 25.5%, 47.6% and 26.9% respectively.the weighting combination mode was taken that counter weight in the middle is major and both ends are auxiliary. Table 1 Results of dynamic balance Kg Head Middle rear weight Concurrent component Effect. The overhaul of the unit was finished on July1,2012.After operation,the critical vibration value of HP-IP rotor was less than 58 m and 1 x, 2 x, 1 y, 2 y shaft vibration value were all less than 61 m.the table 2 shows vibration data of HP-IP rotor.we can see that whether critical vibration value or vibration value with load were in A sector of the national standard.moreover,through vibration data contrast during several start up and speed down process,it can be seen that shaft vibration amplitude and phase have good repetitiveness.therefore,it can be said that vibration state of HP-IP rotor is "stable". Table 2 Vibration data before and after overhaul m working condition 1x 1y 2x 2y Critical vibration 300MW before after before After

4 Applied Mechanics and Materials Vols The rotor bend and treatment condition on the second unit Vibration condition. This unit is also imported type home-made 330MW,shaft system layout,rotor structure are the same as the first unit. The commissioning date of the unit was in May 2010 and its vibration value were all in good condition at that time.later,along with operation time increasing gradually the vibration value were becoming bigger and bigger mainly in the HP-IP rotor critical vibration, its main frequency is fundamental frequency and its property is common forced vibration.such as June 26,2011,during speed up and speed down process,in the critical speed of 1520r/min 1x shaft vibration value was up to 371μm and 1y shaft vibration value was up to 437μm,and the phase were both stable.because of trip and no way to speed up, unit were forced to improve the rate of rising speed to 500r/min and modify vibration protection fixed value to pass the HP-IP rotor critical speed. March 31,2012,the unit stopped for A level maintenance,fig.4 shows bode graph that 1x shaft vibration varied with speed.during the speed down,1x maximal shaft vibration value was 461μm and 2x maximal shaft vibration value was 391μm at 1540r/min. The unit vibration characteristic is similar with the first unit,but critical vibration value already reach dangerous level.another vibration characteristic is that curve is not smooth near the critical speed of the bode and similar to the "burr" shape of the waveform.it is analysed that big shaft vibration would cause rub and impact. Fig.4 1x shaft vibration bode diagram Rotor bend condition and vibration control. From March 31 to May 13 in 2012,during overhaul of the unit,about 0.085mm bend on the medium pressure steam inlet of the HP-IP rotor was found after the cylinder was open[fig.3]. According to operation condition in one year,it is analysed that the reason of rotor bend is internal stress release. Fig.5 Bend of turbine HP-IP rotor

5 898 Applied Mechanics and Materials I Vibration control methods are returning factory for turning and high speed balance.table 3 shows added weight and angle on the high speed test bench.the same as first unit,the weighting combination was taken that counter weight were added in the middle and both ends of the HP-IP rotor at the same time.the counter weight was concurrent component-major,and the counter weight in the middle accounted for 63.37% of total weight. Table 3 Results of dynamic balance Kg Head Middle rear weight Concurrent componen Effect. The overhaul of the unit was finished on May13,2012.After operation,the critical vibration value of HP-IP rotor was less than 141 m and 1 x, 2 x, 1 y, 2 y shaft vibration value were all less than 52 m.the table 4 shows the vibration data of HP-IP rotor.effect of balance can also satisfy the operation requirement. Conclusions Table 4 Vibration data before and after overhaul m working condition 1x 1y 2x 2y Critical vibration before after MW before After Based on vibration tests of two turbine bent rotor,two vibration control methods are put forward,vibration characteristics and balance method are summarized. The vibration frequency of turbine HP-IP rotor whose bent part is in the middle is fundamental frequency, it is mainly manifested in the big critical vibration value,which directly affects the normal unit startup and safe operation.but vibration value increasing is not obvious with load. For certain bent value of turbine HP-IP asymmetric rotor,the vibration control methods are low dynamic balance on site or high dynamic balance after returning factory for turning. In order to eliminate the first order critical vibration,the weighting combination mode concluding in the middle and both ends of turbine HP-IP rotor was taken that counter weight in the middle is major and both ends are auxiliary. References: [1] Wei-xin Shi,Vibration and accident of turbine generator[m].beijing,china Electric Power Press,2008 [2] Guo-an He,Xue-yan Zhang, Yanbo Wang.Thermal power generation, 2012,41(7): [3] Guo-chao Dai.Turbine technology,2008,50(2): [4] Bang-chun Wen,Jia-liu Gu, Song-bo Xia, Zheng Wang.Higher rotor dynamic[m].china Machanical industry Press,1999.

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